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Measuring the Thermal Conductivity of Thermal Grease using the Hot Disk TPS- Applications for Pastes

Thermal greases play an important role in managing the temperature of microprocessors in electronics. They have incredibly low contact resistances, and are able to completely fill any air gaps left between a processor and the heat removal system when they are applied. Furthermore, they are highly versatile, easy to apply, and reliable, making them an excellent tool for keeping electronics cool and operating efficiently. Temperature management is a crucial component in electronics design; as electronics become smaller and more powerful they also produce more heat in a smaller volume, which if not removed effectively will destroy reliability and significantly decrease product lifespan. The Hot Disk Transient Plane Source is a reliable, accurate tool for measuring the thermal conductivity and thermal diffusivity of pastes such as thermal greases. In an excellent example of this type of application, Yi He (2005) from the Intel Corporation used the Hot Disk TPS thermal conductivity equipment to test these parameters in three different thermal greases, and compared his results to those supplied by the manufacturer.

Figure 1. A demonstration of the application of thermal grease to an electronic component1. The thermal grease will help to pull heat away from the processor when it is running.

He (2005) chose the Hot Disk TPS thermal conductivity system for its easy sample set up, fast test times, and accurate results. The TPS performs absolute measurements and does not require a contact agent; the various systems offered cover a thermal conductivity range between 0.005 and 1800 W/mK. Thermtest offers a specialized paste sample holder to facilitate this type of testing (Figure 2). This sample holder is cylindrical in shape, and has an internal height of 9 mm and a diameter of 15 mm. It is used in conjunction with Hot Disk sensor #5465, which has a radius of 3.189 mm. As illustrated in Figure 2, this sample holder sandwiches the sensor in between the paste, and enables excellent thermal contact to be achieved between the sensor and the sample. The sensor acts as both the heating element and the temperature sensor.

Figure 2. A special paste holder is available for testing the thermal conductivity of pastes. On the right is the set up of the holder including the Hot Disk sensor, which is sandwiched in between the two pieces.

He (2005) found that the thermal conductivity values obtained for the thermal greases using the Hot Disk TPS closely mirrored those sent by the supplier that were collected using the hot wire method. He concluded that the amount of filler present in the greases had a substantial impact on the resulting thermal conductivity.

This study is an excellent example of the accuracy and reliability of the Hot Disk TPS for testing the thermal conductivity and thermal diffusivity of pastes. As noted by He (2005) in the closing of his paper, the fast test times and easy set up make the TPS a valuable thermal conductivity instrument for this type of research as it enables rapid development and inspection of new products for electronic packaging. This characteristic makes the TPS system an ideal choice for use in industries where fast paced development is key for maintaining a competitive edge.

Note: For comprehensive results, including specific comparisons between the results from the Hot Disk TPS and the transient hot wire method, please follow the link to this scientific paper in the reference section.

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